Function check_pr_command_prerequisites 

pub fn check_pr_command_prerequisites(
    model_override: Option<&str>,
    repo_root: &Path,
) -> Result<AiCredentialInfo>

Performs combined preflight check for PR creation.

Validates:

• Git repository access
• AI credentials
• GitHub CLI availability and authentication

Returns information about the AI provider that will be used.

repo_root anchors the git-repository and GitHub CLI checks to the injected repository rather than the process current working directory.